Japanese culture: Is it true adult adoption is common in Japan?

True adoption is not that common.

However, if you read the Japanese literature with automatic translation, you will find many more references to "adopted"(養子) than this.

This is due to the fact that Japanese civil law prior to WW2 did not allow one to choose to adopt a woman's surname when they married. If he really wanted to choose a woman's surname, he had to be adopted into a woman's family and married at the same time.

How did a computer scientist such as Geoffrey Hinton manage to win a Nobel Prize in physics when computer science already has its own Nobel Prize equivalent in the Turing Awards?

This custom died out after WW2, but the word 'adopted' remained in the language. It has actually been used as the title of a manga.

This derives from the way surnames are decided when getting married in Japan. In Japan, when people legally marry, they are required to unify their surnames to one of them: around 90% of people unify their surname as a couple using the male surname, while the rest adopt the female surname. This unification with the female surname when getting married is a kind of slang for 'adopted'.

There are two main current examples of this being done: firstly, because a family with a very large estate but no heirs wants to create a new person to manage the estate. The other is for gay people who want to marry in Japan, where same-sex marriage is currently not possible, to be legally recognised as a family. Neither is very common, considering the overall percentage of the population.

Islam is definitely a very anti-LGBTQ religion, so why don't liberals ever stage pro-LGBTQ demonstrations at mosques or at the consulates/embassies of Muslim countries?